Reforming catalyst with chelated promoter

ABSTRACT

A process for preparing a naphtha reforming catalyst has been developed. The process involves the use of a chelating ligand such as ethylenediaminetetraacetic acid (EDTA). The aqueous solution of the chelating ligand and a tin compound is used to impregnate a support, e.g., alumina extrudates. A platinum-group metal is also an essential component of the catalyst. Rhenium may also be a component. A reforming process using the catalyst has enhanced yield, activity, and stability for conversion of naphtha into valuable gasoline and aromatic products.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of application Ser. No. 10/113,125 filedMar. 29, 2002, now U.S. Pat. No. 6,872,300 B1, the contents of which arehereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to a process for preparing a catalyst. Theprocess involves the use of a chelating ligand to form a tin chelatecomplex. The invention also relates to a reforming process using thecatalyst which provides increased selectivity to gasoline components andaromatic products.

Catalytic reforming involves a number of competing processes or reactionsequences. These include dehydrogenation of cyclohexanes to aromatics,dehydroisomerization of alkylcyclopentanes to aromatics,dehydrocyclization of an acyclic hydrocarbon to aromatics, hydrocrackingof paraffins to light products boiling outside the gasoline range,dealkylation of alkylbenzenes and isomerization of paraffins. Some ofthe reactions occurring during reforming, such as hydrocracking whichproduces light paraffin gases, have a deleterious effect on the yield ofproducts boiling in the gasoline range. Process improvements incatalytic reforming thus are targeted toward enhancing those reactionseffecting a higher yield of the gasoline fraction at a given octanenumber.

It is of critical importance that a catalyst exhibits the capabilityboth to initially perform its specified functions efficiently and toperform them satisfactorily for prolonged periods of time. Theparameters used in the art to measure how well a particular catalystperforms its intended function in a particular hydrocarbon reactionenvironment are activity, selectivity and stability. In a reformingenvironment, these parameters are defined as follows:

(1) Activity is a measure of the ability of the catalyst to converthydrocarbon reactants to products at a designated severity level, withseverity level representing a combination of reaction conditions:temperature, pressure, contact time, and hydrogen partial pressure.Activity typically is characterized as the octane number of the pentanesand heavier (“C₅ ⁺”) product stream from a given feedstock at a givenseverity level, or conversely as the temperature required to achieve agiven octane number.

(2) Selectivity refers to the percentage yield of petrochemicalaromatics or C₅ ⁺ gasoline product from a given feedstock at aparticular activity level.

(3) Stability refers to the rate of change of activity or selectivityper unit of time or of feedstock processed. Activity stability generallyis measured as the rate of change of operating temperature per unit oftime or of feedstock to achieve a given C₅ ⁺ product octane, with alower rate of temperature change corresponding to better activitystability, since catalytic reforming units typically operate atrelatively constant product octane. Selectivity stability is measured asthe rate of decrease of C₅ ⁺ product or aromatics yield per unit of timeor of feedstock.

Programs to improve performance of reforming catalysts are beingstimulated by the reformulation of gasoline, following upon widespreadremoval of lead antiknock additive, in order to reduce harmful vehicleemissions. Gasoline-upgrading processes such as catalytic reforming mustoperate at higher efficiency with greater flexibility in order to meetthese changing requirements. Catalyst selectivity is becoming ever moreimportant to tailor gasoline components to these needs while avoidinglosses to lower-value products. The major problem facing workers in thisarea of the art, therefore, is to develop more selective catalysts whilemaintaining effective catalyst activity and stability.

Reforming catalysts containing tin as platinum-group (or Group VIII)modifiers, along with optional third metal promoters such as rhenium,indium, gallium, iridium, etc., are well known in the art. For example,U.S. Pat. No. 3,830,727 discloses a process for catalytic reformingusing a catalyst comprising a platinum, rhenium, and tin, along with ahalogen and a halogen activation step. This catalyst is prepared byimpregnating the support with the desired components. U.S. Pat. No.6,153,090 discloses a process for catalytic reforming using a catalystcomprising at least one group VIII metal, at least one additionalelement selected from the group consisting of germanium, tin, lead,rhenium, gallium, indium, thallium, where the promoter element is addedin the form of an organometallic carboxylate compound containing atleast one organometallic bond such as tributyl tin acetate.

It is also known that chelating ligands can be used to impregnate metalsonto a support. For example, U.S. Pat. No. 4,719,196 discloses preparinga catalyst using a solution containing ethylene diaminetetraacetic acid(EDTA), a noble metal and ammonia. U.S. Pat. No. 5,482,910, which isincorporated herein by reference thereto, discloses a process forpreparing a catalyst using a mixed solution comprising EDTA, a noblemetal, and a promoter metal, such as an alkali earth metal. U.S. Pat.Nos. 6,015,485 and 6,291,394 disclose a process for treating an existingcatalyst with EDTA in order to create a bimodal mesopore structure withalumina at two different crystallite sizes. No references to applicants'knowledge disclose the use of EDTA or a related chelating agent toimpregnate tin onto a catalyst support.

Accordingly, applicants have developed a process for preparing catalystswhich involves the use of a tin chelate complex to impregnate the tincomponent. The process involves preparing a tin solution containing achelating ligand such as EDTA. This solution is heated and then used toimpregnate a refractory oxide support such as alumina. Before or afterthe chelated impregnation, another solution can be used to impregnateplatinum-group metals and any other desired promoter metals such asrhenium. Preferably, the impregnation with the tin chelate is performedat basic conditions, while the impregnation of the other components isperformed at acidic conditions. After impregnation, calcination andreduction provide the desired catalyst.

SUMMARY OF THE INVENTION

This invention relates to a naphtha reforming process, a catalyst forcarrying out the naphtha reforming process, and a process for preparinga naphtha reforming catalyst. Accordingly, one embodiment of theinvention is a process for preparing a naphtha reforming catalystcomprising: a) preparing a first aqueous solution containing a chelatingagent and a tin compound; b) heating said first solution for a time ofabout 5 minutes to about 5 hours at a temperature of about 40° C. toabout 100° C.; c) preparing a second aqueous solution containing aplatinum-group compound and optionally a rhenium compound; e)impregnating a solid refractory oxide support with said first solutionto give a first impregnated solid support; g) impregnating said firstimpregnated solid support with said second solution to give a secondimpregnated solid support; h) calcining the second impregnated solidsupport at a temperature of about 300° C. to about 850° C. for a time ofabout 10 minutes to about 18 hours to give a calcined catalyst; and i)reducing the calcined catalyst at a temperature of about 300° to about850° C. for a time of about 30 minutes to about 18 hours under areducing atmosphere, thereby providing said catalyst suitable fornaphtha reforming.

In another embodiment, the invention relates to a process for thecatalytic reforming of a naphtha feedstock which comprises contactingthe feedstock at reforming conditions with a catalyst comprising aparticulate inorganic oxide support having dispersed thereon a tincomponent, a platinum-group metal component, and optionally a rheniumcomponent; the catalyst characterized in that the tin component isdeposited on the support by impregnation using a tin chelate complex andis uniformly distributed throughout the support.

In a further embodiment, the invention relates to a catalyst effectivefor naphtha reforming comprising a particulate refractory inorganicoxide support having dispersed thereon a tin component in an amount ofabout 0.01 to about 0.5 mass-% on an elemental basis, a platinumcomponent in an amount of about 0.01 to about 2 mass-% on an elementalbasis, and optionally a rhenium component in an amount of about 0.05 toabout 5 mass-% on an elemental basis. The catalyst is characterized inthat the tin is uniformly distributed and the platinum-group metal isuniformly distributed; the tin being dispersed on the support with animpregnation using a tin chelate complex.

Additional objects, embodiments and details of this invention can beobtained from the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents plots of C₅ ⁺ liquid yields as a function of catalystlife for various catalysts incorporating tin by different methods.

FIG. 2 presents plots of average reactor block temperaturescorresponding to catalyst activity as a function of catalyst life forvarious tin incorporation methods.

DETAILED DESCRIPTION OF THE INVENTION

The catalyst of the present invention has particular utility as ahydrocarbon conversion catalyst. The hydrocarbon which is to beconverted is contacted with the catalyst at hydrocarbon-conversionconditions, which include a temperature of from 40° to 1000° C., apressure of from atmospheric to 200 atmospheres absolute and liquidhourly space velocities from about 0.1 to 100 hr⁻¹. The catalyst isparticularly suitable for catalytic reforming of gasoline-rangefeedstocks, and also may be used for, inter alia, dehydrocyclization,isomerization of aliphatics and aromatics, dehydrogenation,hydrocracking, disproportionation, dealkylation, alkylation,transalkylation, and oligomerization.

In the preferred catalytic reforming embodiment, hydrocarbon feedstockand a hydrogen-rich gas are preheated and charged to a reforming zonecontaining typically two to five reactors in series. Suitable heatingmeans are provided between reactors to compensate for the netendothermic heat of reaction in each of the reactors. Reactants maycontact the catalyst in individual reactors in either upflow, downflow,or radial flow fashion, with the radial flow mode being preferred. Thecatalyst is contained in a fixed-bed system or, preferably, in amoving-bed system with associated continuous catalyst regeneration.Alternative approaches to reactivation of deactivated catalyst are wellknown to those skilled in the art, and include semi-regenerativeoperation in which the entire unit is shut down for catalystregeneration and reactivation or swing-reactor operation in which anindividual reactor is isolated from the system, regenerated andreactivated while the other reactors remain on-stream. The preferredcontinuous catalyst regeneration in conjunction with a moving-bed systemis disclosed, inter alia, in U.S. Pat. Nos. 3,647,680; 3,652,231;3,692,496 and 4,832,921, all of which are incorporated herein byreference.

Effluent from the reforming zone is passed through a cooling means to aseparation zone, typically maintained at about 0° to 65° C., wherein ahydrogen-rich gas is separated from a liquid stream commonly called“unstabilized reformate”. The resultant hydrogen stream can then berecycled through suitable compressing means back to the reforming zone.The liquid phase from the separation zone is typically withdrawn andprocessed in a fractionating system in order to adjust the butaneconcentration, thereby controlling front-end volatility of the resultingreformate.

Reforming conditions applied in the reforming process of the presentinvention include a pressure selected within the range of about 100 kPato 7 MPa (abs). Particularly good results are obtained at low pressure,namely a pressure of about 350 to 2500 kPa (abs). Reforming temperatureis in the range from about 315° to 600° C., and preferably from about425° to 565° C. As is well known to those skilled in the reforming art,the initial selection of the temperature within this broad range is madeprimarily as a function of the desired octane of the product reformateconsidering the characteristics of the charge stock and of the catalyst.Ordinarily, the temperature then is thereafter slowly increased duringthe run to compensate for the inevitable deactivation that occurs toprovide a constant octane product. Sufficient hydrogen is supplied toprovide an amount of about 1 to about 20 moles of hydrogen per mole ofhydrocarbon feed entering the reforming zone, with excellent resultsbeing obtained when about 2 to about 10 moles of hydrogen are used permole of hydrocarbon feed. Likewise, the liquid hourly space velocity(LHSV) used in reforming is selected from the range of about 0.1 toabout 20 hr⁻¹, with a value in the range of about 1 to about 5 hr⁻¹being preferred.

The hydrocarbon feedstock that is charged to this reforming systempreferably is a naphtha feedstock comprising naphthenes and paraffinsthat boil within the gasoline range. The preferred feedstocks arenaphthas consisting principally of naphthenes and paraffins, although,in many cases, aromatics also will be present. This preferred classincludes straight-run gasolines, natural gasolines, synthetic gasolines,and the like. As an alternative embodiment, it is frequentlyadvantageous to charge thermally or catalytically cracked gasolines,partially reformed naphthas, or dehydrogenated naphthas. Mixtures ofstraight-run and cracked gasoline-range naphthas can also be used toadvantage. The gasoline-range naphtha charge stock may be a full-boilinggasoline having an initial ASTM D-86 boiling point of from about 40° to80° C. and an end boiling point within the range of from about 160° to220° C., or may be a selected fraction thereof which generally will be ahigher-boiling fraction commonly referred to as a heavy naphtha—forexample, a naphtha boiling in the range of 100° to 200° C. If thereforming is directed to production of one or more of benzene, tolueneand xylenes, the boiling range may be principally or substantiallywithin the range of 60° to 150° C. In some cases, it is alsoadvantageous to process pure hydrocarbons or mixtures of hydrocarbonsthat have been recovered from extraction units—for example, raffinatesfrom aromatics extraction or straight-chain paraffins—which are to beconverted to aromatics.

It is generally preferred to utilize the present invention in asubstantially water-free environment. Essential to the achievement ofthis condition in the reforming zone is the control of the water levelpresent in the feedstock and the hydrogen stream which is being chargedto the zone. Best results are ordinarily obtained when the total amountof water entering the conversion zone from any source is held to a levelless than 50 ppm and preferably less than 20 ppm, expressed as weight ofequivalent water in the feedstock. In general, this can be accomplishedby careful control of the water present in the feedstock and in thehydrogen stream. The feedstock can be dried by using any suitable dryingmeans known to the art such as a conventional solid adsorbent having ahigh selectivity for water; for instance, sodium or calcium crystallinealuminosilicates, silica gel, activated alumina, molecular sieves,anhydrous calcium sulfate, high surface area sodium, and the likeadsorbents. Similarly, the water content of the feedstock may beadjusted by suitable stripping operations in a fractionation column orlike device. In some cases, a combination of adsorbent drying anddistillation drying may be used advantageously to effect almost completeremoval of water from the feedstock. Preferably, the feedstock is driedto a level corresponding to less than 20 ppm of H₂O equivalent.

It is preferred to maintain the water content of the hydrogen streamentering the hydrocarbon conversion zone at a level of about 10 to about20 volume ppm or less. In the cases where the water content of thehydrogen stream is above this range, this can be convenientlyaccomplished by contacting the hydrogen stream with a suitable desiccantsuch as those mentioned above at conventional drying conditions.

It is a preferred practice to use the present invention in asubstantially sulfur-free environment. Any control means known in theart may be used to treat the naphtha feedstock which is to be charged tothe reforming reaction zone. For example, the feedstock may be subjectedto adsorption processes, catalytic processes, or combinations thereof.Adsorption processes may employ molecular sieves, high surface areasilica-aluminas, carbon molecular sieves, crystalline aluminosilicates,activated carbons, high surface area metallic containing compositions,such as nickel or copper and the like. It is preferred that thesefeedstocks be treated by conventional catalytic pre-treatment methodssuch as hydrorefining, hydrotreating, hydrodesulfurization, etc., toremove substantially all sulfurous, nitrogenous and water-yieldingcontaminants therefrom, and to saturate any olefins that may becontained therein. Catalytic processes may employ traditional sulfurreducing catalyst formulations known to the art including refractoryinorganic oxide supports containing metals selected from the groupcomprising Group VI-B(6), Group II-B(12), and Group VIII(IUPAC 8-10) ofthe Periodic Table.

As stated, the present invention relates to a process for preparing acatalyst. The catalyst comprises a solid refractory oxide support havingdispersed thereon a tin component, at least one platinum group metalcomponent and optionally a modifier metal such as rhenium. The supportcan be any of a number of well-known supports in the art includingaluminas, silica/alumina, silica, titania, zirconia, and zeolites. Thealuminas which can be used as support include gamma alumina, thetaalumina, delta alumina, and alpha alumina with gamma and theta aluminabeing preferred. Included among the aluminas are aluminas which containmodifiers such as tin, zirconium, titanium and phosphate. The zeoliteswhich can be used include: faujasites, zeolite beta, L-zeolite, ZSM-5,ZSM-8, ZSM-11, ZSM-12 and ZSM-35. The supports can be formed in anydesired shape such as spheres, pills, cakes, extrudates, powders,granules, etc. and they may be utilized in any particular size.

One way of preparing a spherical alumina support is by the well knownoil drop method which is described in U.S. Pat. No. 2,620,314 which isincorporated by reference. The oil drop method comprises forming analuminum hydrosol by any of the techniques taught in the art andpreferably by reacting aluminum metal with hydrochloric acid; combiningthe hydrosol with a suitable gelling agent; and dropping the resultantmixture into an oil bath maintained at elevated temperatures. Thedroplets of the mixture remain in the oil bath until they set and formhydrogel spheres. The spheres are then continuously withdrawn from theoil bath and typically subjected to specific aging and drying treatmentsin oil and ammoniacal solutions to further improve their physicalcharacteristics. The resulting aged and gelled spheres are then washedand dried at a relatively low temperature of about 80° to 260° C. andthen calcined at a temperature of about 455° to 705° C. for a period ofabout 1 to about 20 hours. This treatment effects conversion of thehydrogel to the corresponding crystalline gamma alumina. If thetaalumina is desired, then the hydrogel spheres are calcined at atemperature of about 950° to about 1100° C.

An alternative form of carrier material is a cylindrical extrudate,preferably prepared by mixing the alumina powder with water and suitablepeptizing agents such as HCl until an extrudable dough is formed. Theamount of water added to form the dough is typically sufficient to givea loss on ignition (LOI) at 500° C. of about 45 to 65 mass-%, with avalue of 55 mass-% being preferred. The acid addition rate is generallysufficient to provide 2 to 7 mass-% of the volatile-free alumina powderused in the mix, with a value of 3 to 4 mass-% being preferred. Theresulting dough is extruded through a suitably sized die to formextrudate particles. These particles are then dried at a temperature ofabout 260° to about 427° C. for a period of about 0.1 to 5 hours to formthe extrudate particles. It is preferred that the refractory inorganicoxide comprises substantially pure alumina having an apparent bulkdensity of about 0.6 to about 1 g/cc and a surface area of about 150 to280 m²/g (preferably 185 to 235 m²/g, at a pore volume of 0.3 to 0.8cc/g). A typical substantially pure alumina has been characterized inU.S. Pat. No. 3,852,190 and U.S. Pat. No. 4,012,313 as a by-product froma Ziegler higher alcohol synthesis reaction as described in Ziegler'sU.S. Pat. No. 2,892,858.

A Group IVA(IUPAC 14) metal component is an essential ingredient of thecatalyst of the present invention. Of the Group IVA(IUPAC 14) metals,germanium and tin are preferred and tin is especially preferred. Thiscomponent may be present as an elemental metal, as a chemical compoundsuch as the oxide, sulfide, halide, oxychloride, etc., or as a physicalor chemical combination with the porous carrier material and/or othercomponents of the catalytic composite. Preferably, a substantial portionof the Group IVA(IUPAC 14) metal exists in the finished catalyst in anoxidation state above that of the elemental metal. The Group IVA(TUPAC14) metal component, which is preferably tin, optimally is utilized inan amount sufficient to result in a final catalytic composite containingabout 0.01 to about 5 mass-% metal, calculated on an elemental basis,with best results obtained at a level of about 0.1 to about 0.5 mass-%metal.

The Group IVA(IUPAC 14) metal or metals are dispersed onto the desiredsupport as follows. First, an aqueous solution of a chelating ligand andat least one soluble, decomposable metal promoter compound is preparedto give a promoter metal chelate complex. Preferably, the metal compoundis a tin compound. More preferably, the tin compound is a tin salt.Examples of suitable tin salts or water-soluble compounds of tin includewithout limitation stannous bromide, stannous chloride, stannicchloride, stannic chloride pentahydrate, stannic chloride tetrahydrate,stannic chloride trihydrate, stannic chloride diamine, stannictrichloride bromide, stannic chromate, stannous fluoride, stannicfluoride, stannic iodide, stannic sulfate, stannic tartrate, stannicoxalate, stannic acetate and the like compounds. The utilization of atin salt in the form of a chloride compound, such as stannous or stannicchloride is particularly preferred since it facilitates theincorporation of both the tin component and at least a minor amount of ahalogen component in a single step. Highly preferred is a salt with tinhaving a plus two oxidation state.

The chelating ligands which can be used in the process of this inventioninclude amino acids which upon decomposing do not leave overlydetrimental components on the support, e.g., sulfur. Specific examplesof these amino acids include ethylenediaminetetraacetic acid,nitrilotriacetic acid, N-methylaminodiacetic acid, iminodiacetic acid,glycine, alanine, sarcosine, α-aminoisobutyric acid,N,N-dimethylglycine, α,β-diaminopropionate, aspartate, glutamate,histidine, and methionine.

The chelate-metal complex solution, which is preferably a chelate-tincomplex solution, is heated for a time of about 5 minutes to about 5hours at a temperature of about 40° to about 100° C. or its boilingpoint. The ratio of chelating ligand to the metal salt will vary fromabout 1 to about 8 and preferably from about 1.5 to about 4.

The chelate-metal solution described above may also contain a basiccompound selected from the group consisting of ammonium hydroxide andquaternary ammonium compounds having the formula NR₁R₂R₃R₄ ⁺X⁻ where R₁,R₂, R₃, R₄ are each separately methyl, ethyl, propyl, butyl or t-butyland X is hydroxide. The purpose of adding one or more of these basiccompounds is to adjust the pH of the solution in order to vary thedistribution of the metals. That is, in some cases it may be desirableto have a uniform distribution of the metals whereas in other cases agreater concentration on the surface may be desirable. Further, thedistribution of the IVA(IUPAC 14) metal may be different from thedistribution of the platinum-group or other promoter metal. For thepresent invention, it is preferred that the tin component andplatinum-group components are uniformly distributed throughout thecatalyst.

The chelate-metal complex solution is now used to deposit the metal ontothe support by means well known in the art. Examples of said meansinclude spray impregnation and evaporative impregnation. Sprayimpregnation involves taking a small volume of the mixed solution andspraying it over the support while the support is moving. When thespraying is over, the wetted support can be transferred to otherapparatus for drying or finishing steps.

In one embodiment of the invention, the refractory oxide support isfirst impregnated with the tin chelate complex, and then impregnatedwith a platinum-group component. In another embodiment of the invention,the tin chelate complex is impregnated after the platinum-groupcomponent. Note that the impregnation steps may overlap as well.Preferably, once at least 80 mass-% of the platinum-group component hasbeen impregnated onto the support then immediately thereafterimpregnation with a tin chelate complex can begin. Alternatively, whentwo distinct impregnation procedures are performed then the support maybe dried and/or calcined in between procedures as needed under thedrying and calcination conditions listed hereinafter. Preferably, thecalcination after the first distinct impregnation is sufficient toconvert the tin to a tin-oxide compound.

An essential ingredient of the catalyst is a dispersed platinum-groupcomponent. This platinum-group component may exist within the finalcatalytic composite as a compound such as an oxide, sulfide, halide,oxyhalide, etc., in chemical combination with one or more of the otheringredients of the composite or as an elemental metal. It is preferredthat substantially all of this component is present in the elementalstate and is uniformly dispersed within the support material. Thiscomponent may be present in the final catalyst composite in any amountwhich is catalytically effective, but relatively small amounts arepreferred. Of the platinum-group metals which can be dispersed on thedesired support, preferred metals are rhodium, palladium, platinum, andplatinum being most preferred. Platinum generally comprises about 0.01to about 2 mass-% of the final catalytic composite, calculated on anelemental basis. Excellent results are obtained when the catalystcontains about 0.05 to about 1 mass-% of platinum.

This platinum component may be incorporated into the catalytic compositein any suitable manner, such as coprecipitation or cogelation,ion-exchange, or impregnation, in order to effect a uniform dispersionof the platinum component within the carrier material. The preferredmethod of preparing the catalyst involves the utilization of a soluble,decomposable compound of platinum to impregnate the carrier material.For example, this component may be added to the support by comminglingthe latter with an aqueous solution of chloroplatinic acid. Otherwater-soluble compounds of platinum may be employed in impregnationsolutions and include ammonium chloroplatinate, bromoplatinic acid,platinum dichloride, platinum tetrachloride hydrate, platinumdichlorocarbonyl dichloride, dinitrodiaminoplatinum, etc. Theutilization of a platinum chloride compound, such as chloroplatinicacid, is preferred since it facilitates the incorporation of both theplatinum component and at least a minor quantity of the halogencomponent in a single step. Best results are obtained in the preferredimpregnation step if the platinum compound yields complex anionscontaining platinum in acidic aqueous solutions. Hydrogen chloride orthe like acid is also generally added to the impregnation solution inorder to further facilitate the incorporation of the halogen componentand the distribution of the metallic component. In addition, it isgenerally preferred to impregnate the carrier material after it has beencalcined in order to minimize the risk of washing away the valuableplatinum compounds; however, in some cases, it may be advantageous toimpregnate the carrier material when it is in a gelled state.

Rhenium is an optional metal promoter of the catalyst. The platinum andrhenium components of the terminal catalytic composite may be compositedwith the refractory inorganic oxide in any manner which results in apreferably uniform distribution of these components such ascoprecipitation, cogelation, coextrusion, ion exchange or impregnation.Alternatively, non-uniform distributions such as surface impregnationare within the scope of the present invention. The preferred method ofpreparing the catalytic composite involves the utilization of solubledecomposable compounds of platinum and rhenium for impregnation of therefractory inorganic oxide in a relatively uniform manner. For example,the platinum and rhenium components may be added to the refractoryinorganic oxide by commingling the latter with an aqueous solution ofchloroplatinic acid and thereafter an aqueous solution of perrhenicacid. Other water-soluble compounds or complexes of platinum and rheniummay be employed in the impregnation solutions. Typical decomposablerhenium compounds which may be employed include ammonium perrhenate,sodium perrhenate, potassium perrhenate, potassium rhenium oxychloride,potassium hexachlororhenate (IV), rhenium chloride, rhenium heptoxide,and the like compounds. The utilization of an aqueous solution ofperrhenic acid is preferred in the impregnation of the rheniumcomponent.

As heretofore indicated, any procedure may be utilized in compositingthe platinum component and rhenium component with the refractoryinorganic oxide as long as such method is sufficient to result inrelatively uniform distributions of these components. Accordingly, whenan impregnation step is employed, the platinum component and rheniumcomponent may be impregnated by use of separate impregnation solutionsor, as is preferred, a single impregnation solution comprisingdecomposable compounds of platinum component and rhenium component. Itshould be noted that irrespective of whether single or separateimpregnation solutions are utilized, hydrogen chloride, nitric acid, orthe like acid may be also added to the impregnation solution orsolutions in order to further facilitate uniform distribution of theplatinum and rhenium components throughout the refractory inorganicoxide. Additionally, it should be indicated that it is generallypreferred to impregnate the refractory inorganic oxide after it has beencalcined in order to minimize the risk of washing away valuable platinumand rhenium compounds; however, in some cases, it may be advantageous toimpregnate refractory inorganic oxide when it is in a gelled, plasticdough or dried state. If two separate impregnation solutions areutilized in order to composite the platinum component and rheniumcomponent with the refractory inorganic oxide, separate oxidation andreduction steps may be employed between application of the separateimpregnation solutions. Additionally, halogen adjustment steps may beemployed between application of the separate impregnation solutions.Such halogenation steps will facilitate incorporation of the catalyticcomponents and halogen component into the refractory inorganic oxide.

It may be desirable to use the methods of U.S. Pat. No. 5,482,910, whichhas been incorporated by reference, to use chelating agents toincorporate the platinum-group and/or rhenium components in a dualcomponent, or co-impregnation type manner along with a chelate tincomplex, or independent of the complex.

Irrespective of its exact formation, the dispersion of platinumcomponent and rhenium component must be sufficient so that the platinumcomponent comprises, on an elemental basis, from about 0.01 to about 2mass-% of the finished catalytic composite. Additionally, there must besufficient rhenium component present to comprise, on an elemental basis,from about 0.01 to about 5 mass-% of the finished composite.

In addition to the catalytic components described above, othercomponents may be added to the catalyst. For example, a modifier metalselected from the group consisting of germanium, lead, indium, gallium,iridium, lanthanum, cerium, phosphorous, cobalt, nickel, iron andmixtures thereof may be added to the catalyst.

One particular method of evaporative impregnation involves the use of asteam-jacketed rotary dryer. In this method the support is immersed inthe impregnating solution which has been placed in the dryer and thesupport is tumbled by the rotating motion of the dryer. Evaporation ofthe solution in contact with the tumbling support is expedited byapplying steam to the dryer jacket. The impregnated support is thendried at a temperature of about 60° to about 300° C. and then calcinedat a temperature of about 300° to about 850° C. for a time of about 30minutes to about 18 hours to give the calcined catalyst. Finally, thecalcined catalyst is reduced by heating the catalyst under a reducingatmosphere, preferably dry hydrogen, at a temperature of about 300° toabout 850° C. for a time of about 30 minutes to about 18 hours. Thisensures that the metal is in the metallic or zerovalent state.

An optional step in the process of this invention involves halogenation,which is preferably oxychlorination, of the reduced catalyst describedabove. If such a step is desired, the catalyst is placed in a reactorand a gaseous stream containing a halogen, which is preferably chlorideor chlorine, is flowed over the catalyst at a flow rate of about 0.9kg/hr to about 18.1 kg/hr, at a temperature of about 300° to about 850°C. for a time of about 10 minutes to about 12 hours. The gaseous streamcan be a hydrogen chloride/chlorine stream, a water/HCl stream, awater/Cl₂ stream or a chlorine stream. The purpose of this step is toprovide optimum dispersion of the Group VIII and provide a certainamount of halide, preferably chloride, on the final catalyst. Thehalogen content of the final catalyst should be such that there issufficient halogen to comprise, on an elemental basis, from about 0.1 toabout 10 mass-% of the finished composite.

Optionally, the catalytic composite may be subjected to a presulfidingstep. The optional sulfur component may be incorporated into thecatalyst by any known technique.

The following examples are presented in illustration of this inventionand are not intended as undue limitations on the generally broad scopeof the invention as set out in the appended claims.

EXAMPLE 1

Tin was added to the support when as part of the forming process calledextrusion, or preferably co-extrusion. 2500 g of alumina powder(commercially available under the trade names Catapal B and/or Versal250) was added to a mixer. A solution was prepared using 60.8 g nitricacid (67.5% HNO₃) with 220 g deionized water, followed by the additionof 5.91 g of tin tartrate, and the solution was stirred. The solutionwas added to the alumina powder in the mixer, and mulled to make a doughsuitable for extrusion. The dough was extruded through a die plate toform extrudate particles. The extrudate particles were dried at on abelt calciner operating with a first zone at 370° C. for about 15minutes and a second zone at 620° C. for about 30 minutes.

The extrudate particles were placed in a rotary evaporator and heated to60° C. A solution comprising deionized water, hydrochloric acid,chloroplatinic acid, and perrhenic acid was added to the rotaryevaporator and temperature was raised to 100° C. and the support rolledfor 5 hours. Next the impregnated support was heated to a temperature of525° C. in dry air. When the temperature was reached, an air streamcontaining HCl and Cl₂ was flowed through the catalyst for 6 hours.Finally, the catalyst was reduced by flowing pure hydrogen over thecatalyst at a temperature of 510° C. for 2.5 hours.

Analysis of the catalyst showed it to contain 0.25 mass-% Pt and 0.25mass-% Re and 0.1 mass-% Sn. The platinum, rhenium and tin were evenlydistributed throughout the support. This catalyst was identified asCatalyst A.

EXAMPLE 2

A spherical alumina support was prepared by the well-known oil droppingmethod, per U.S. Pat. No. 3,929,683. A tin component was incorporated inthe support by commingling a tin component precursor with the aluminahydrosol and thereafter gelling the hydrosol. The catalyst particleswere then dried at 600° C. for about 2 hours.

This support was placed in a rotary evaporator and heated to 60° C. Asolution comprising deionized water, hydrochloric acid, chloroplatinicacid, and perrhenic acid was added to the rotary evaporator andtemperature was raised to 100° C. and the support rolled for 5 hours.Next the impregnated support was heated to a temperature of 525° C. indry air. When the temperature was reached, an air stream containing HCland C1₂ was flowed through the catalyst for 6 hours. Finally, thecatalyst was reduced by flowing pure hydrogen over the catalyst at atemperature of 510° C. for 2.5 hours.

Analysis of the catalyst showed it to contain 0.25 mass-% Pt and 0.25mass-% Re and 0.3 mass-% Sn. The platinum, rhenium and tin were evenlydistributed throughout the support. This catalyst was identified asCatalyst B.

EXAMPLE 3

A tin-EDTA solution was prepared by combining in a flask 300 g ofdeionized water, 1.42 g of ammonium hydroxide (concentration 29.6%NH4OH), and 0.88 g of EDTA and stirred to dissolve EDTA. Then 0.3392 gof tin chloride (Sn Cl₂*2H₂O) was added while stirring the solution andheated to 60° C. to dissolve.

A second solution was prepared by the addition to 300 g of deionizedwater of 14.21 g of hydrochloric acid (37.6% HCl) and 17.48 ml ofchloroplatinic acid (H₂PtCl₆ solution with a Pt concentration 27.6mg/ml). Next was added 14.65 ml of perrhenic acid (HReO₄ solution with aRe concentration 32.8 mg/ml).

178.92 Grams of gamma alumina extrudates was placed in a rotaryevaporator and heated to 60° C. The tin-EDTA solution was added to thegamma alumina in the rotary evaporator and the temperature was raised to100° C. and the support rolled for 5 hours.

Then, the second solution was added to the rotary evaporator. The secondsolution was evaporated during 5 hours. Next the impregnated support washeated to a temperature of 525° C. in dry air. When the temperature wasreached, an air stream containing HCl and Cl₂ was flowed through thecatalyst for 6 hours. Finally, the catalyst was reduced by flowing purehydrogen over the catalyst at a temperature of 510° C. for 2.5 hours.

Analysis of the catalyst showed it to contain 0.25 mass-% Pt and 0.25mass-% Re and 0.1 mass-% Sn. The platinum, rhenium and tin were evenlydistributed throughout the support. This catalyst was identified asCatalyst C.

EXAMPLE 4

Catalysts A, B, C were tested for catalytic reforming ability in a pilotplant using a typical naphtha feedstock available from the westernUnited States as follows. Process conditions were selected to achieve aresearch octane number (RONC) of 100. Pressure was 1379 kPa (200 psig),hydrogen to hydrocarbon mole ratio was 1.5, and liquid hourly spacevelocity was 2.5 hr⁻¹. Catalyst life was measured by the prevailingindustry standard using Barrels of feed Per Cubic Foot of catalyst, orBPCF, as shown in FIG. 1 and FIG. 2. First, FIG. 1 presents plots of C₅⁺ liquid yields as a function of catalyst life. Second, FIG. 2 presentsplots of average reactor block temperatures corresponding to catalystactivity as a function of catalyst life. The results from this test aresummarized in the table below indicating equivalent start of runactivity and yield at 12.5 BPCF.

TABLE Catalyst ID Activity, ° C. Yield, mass-% A 515 83.4 B 526 83.9 C514 84.3

The data indicate that Catalyst C had the best yield and best activity.

1. A catalyst effective for naphtha reforming consisting essentially ofa particulate refractory inorganic oxide support having distributedthroughout a stannous component, a platinum-group metal component, and arhenium component; the catalyst characterized in that the tin and theplatinum-group metal are uniformly distributed throughout the support.2. The catalyst of claim 1 wherein the support is alumina.
 3. Thecatalyst of claim 1 wherein the stannous component is present in anamount of about 0.01 to about 0.5 mass- % on an elemental basis.
 4. Thecatalyst of claim 1 wherein the platinum-group metal component isplatinum, which is present in an amount of about 0.01 to about 2 mass- %on an elemental basis.
 5. The catalyst of claim 1 wherein the rheniumcomponent is present in an amount of about 0.05 to about 5 mass- % on anelemental basis.
 6. A catalyst effective for naphtha reformingconsisting essentially of a particulate refractory inorganic oxidesupport having dispersed thereon a stannous component in an amount ofabout 0.01 to about 0.5 mass- % on an elemental basis, a platinumcomponent in an amount of about 0.01 to about 2 mass- % on an elementalbasis, and a rhenium component in an amount of about 0.05 to about 5mass- % on an elemental basis; the catalyst characterized in that thetin and the platinum are uniformly distributed; wherein the uniformdistribution of the tin is characterized as the uniform distributionprepared by a process comprising: a) preparing a first aqueous solutioncontaining a chelating agent and a +2 tin salt; b) heating said firstsolution for a time of about 5 minutes to about 5 hours at a temperatureof about 40° to about 100° C.; c) preparing a second aqueous solutioncontaining chloroplatinic acid and perhennic acid; d) impregnating saidfirst solution onto a solid refractory oxide support to give a firstimpregnated solid support; e) impregnating said first impregnated solidsupport with said second solution to give a second impregnated solidsupport; f) calcining the second impregnated solid support at atemperature of about 300° to about 850° C. for a time of about 10minutes to about 18 hours to give a calcined catalyst; and g) reducingthe calcined catalyst at a temperature of about 300° to about 850° C.for a time of about 30 minutes to about 18 hours under reducingconditions, thereby providing said catalyst suitable for naphthareforming.
 7. The catalyst of claim 6 wherein the chelating agent isselected from the group consisting of ethylenediaminetetraacetic acid,nitrilotriacetic acid, N-methylaminodiacetic acid, iminodiacetic acid,glycine, alanine, sarcosine, α-aminoisobutyric acid,N,N-dimethylglycine, α,β-diaminopropionate, aspartate, glutamate,histidine, and methionine.
 8. The catalyst of claim 7 wherein thechelating agent is ethylenediaminetetraacetic acid.
 9. The catalyst ofclaim 6 further characterized in that the first solution contains abasic compound selected from the group consisting of ammonium hydroxideand quaternary ammonium compounds having the formula NR₁ R₂R₃R₄ ⁺X⁻whereR₁, R₂, R₃, R₄ are each separately methyl, ethyl, propyl, butyl ort-butyl and X is hydroxide.
 10. The catalyst of claim 6 wherein thesupport is alumina.
 11. A catalyst effective for naphtha reformingconsisting essentially of a particulate refractory inorganic oxidesupport having distributed throughout a stannous component, aplatinum-group metal component, a rhenium component, and a halogencomponent; the catalyst characterized in that the tin and theplatinum-group metal are uniformly distributed throughout the support.12. The catalyst of claim 11 wherein the halogen component is present inan amount of about 0.1 to about 10 mass- % on an elemental basis. 13.The catalyst of claim 11 wherein the platinum-group metal component isplatinum, which is present in an amount of about 0.01 to about 2 mass- %on an elemental basis.
 14. The catalyst of claim 11 wherein the rheniumcomponent is present in an amount of about 0.05 to about 5 mass- % on anelemental basis.